rc car detailed analysis

Basic Structure

DOWN LEFTRIGHT

UPRX

TX

RFReceiver

Robot

RX

RFTransmitter

RX

TX

RX

The Transmitter

MA

X23

2

RX

TX

RXRX

TX

RX

AT

89C

2051

HT

12E

BIT #1

BIT #2

BIT #3

BIT #4

The Receiver (BOT)

L29

3D

AT

89C

2051

BIT #1

BIT #2

BIT #3

BIT #4

HT

12D

BIT #1

BIT #2

BIT #3

BIT #4

Left Motor

Right Motor

The Application

Sender ThreadEncode data usingselected protocol

Data flow

The software encodes the motor data using the selected protocols upon receiving interrupt from the user and then the sender thread transfers this data to the serial port.

The 8051 receiving serial data converts it into parallel and passes it to ht12e encoder.

The encoder then encodes this 4 bit data into transferable format and transfers the data to the transmitter.

The receiver receives this data and ht12d decoder decodes it into 4-bit parallel data.

This data is recognized by the 8051 microcontroller and it thus controls the motors using the l293d motor driver ic.

Protocols

3 bit address 1 bit data mode (3-1 protocol)

1 0 1 1

Address

Main memory (Remote)

1 0 1 1 1 0 1 1

Main memory (Remote)Data

(encoded)

Data

This means in the main memory set the 3rd bit (011) (starting from 0) as 1.In order to transfer full 8 bit data a total of 8 transmissions are needed.Example : In order to transfer 10110011 , the following data needs to be sent –1000 , 1001 , 0010 , 0011 , 1100 , 1101 , 0110 , 1111

Over 4-bit RF line

Protocols

2 bit address 2 bit data mode (2-2 protocol)

1 0 1 1

Address

Main memory (Remote)

1 0 1 1 1 0 1 1Data

(encoded)

Data

Address 11 means 7th and 8th bit thus data10 will be placed at 7th and 8th bit in the mainmemory.In order to transfer full 8 bit data a total of 4 transmissions are needed.Example : In order to transfer 10110011 , the following data needs to be sent –1100 , 0001 , 1110 , 1011

Over 4-bit RF line

1 0 1 1 1 0 1 1

Address lookup

0000011011

Advantages of these protocols

3-1 protocol is slower than 2-2 protocol but is more efficient in transferring single bits.

These protocols ensure there is no loss of data , while transferring large data over small data packet size.

2-2 protocol is more efficient in this case as it modifies 2 bits all together . One motors need 2-bit data. Thus for controlling 2 motors a total of 4 bits in the main memory will be needed hence the data will be transferred in only 2 transmissions (with 2-2 protocol) or in 4 transmissions (with 3-1 protocol).

The remaining 4 bits can be used for some other data like headlights and horn (Note : I am limited to one direction data transfer).

Software architecture

Sender ThreadEncode data usingselected protocol

Sender ThreadEncode data usingselected protocolThe user can either control the robot using

Arrow keys or buttons. It also has bit edit Functionality to send custom data to theRobot. As soon as the user presses a arrow key an the sender thread calls the Required command sequence and sends to the serial port. (Note : only starting4 – bits are used)

Turn left : send 00000000delaysend 00001010delay

Turn Right : send 00000000delaysend 00000101delay

Forward : send 00000000delaysend 00000110delay

Backward : send 00000000delaysend 00001001delay

Precautions of motor control

The dc motors connected to the motor driver cannot be turned instantaneously rather a delay (minimum of 50 ms) is required while turning from one direction to another.

Screenshot